The invention relates to novel phospholipid-analogous compounds which can be employed as liposome constituents for transporting pharmaceuticals, as solubilizers for pharmaceuticals of low solubility in water and also as active ingredients themselves for disorders such as cancer and leishmaniosis, to liposomes containing these novel compounds, to pharmaceutical compositions which contain these liposomes, and to processes for producing pharmaceuticals.
The invention relates in particular to phosphatidyl compounds which contain a defined hydrophilic radical, and to liposomes which have a shortened or lengthened lifespan in the serum and can be taken up specifically by particular cells, for example tumour cells.
The retention time of conventional liposomes in the serum is up to 5 hours. However, it is desirable, especially when liposomes are used as carriers of active pharmaceutical ingredients, for the liposome retention time in the blood circulation to be as long as possible, but especially in conjunction with uptake in selected target cells.
Hence the so-called stealth liposomes which have a lengthened lifespan were developed. These stealth liposomes have a structure based on phosphatidyl compounds which contain an extended polyethylene glycol residue. The polyethylene glycol residue proved to be most effective for the desired lengthened lifespan with molecular weights between 2000 and 3000. A considerable disadvantage of these stealth liposomes and of the phosphatidyl compounds with polyethylene glycol residue is, however, that they are not accurately defined compounds because the polyethylene glycol residues have different chain lengths. However, the so-called stealth liposomes always have, as a consequence of the phosphate radical, a negative surface charge in the liposome membrane. The object of our own earlier patent application 196 22 224.9 was therefore to provide compounds which increase the lifespan of liposomes and have a composition which can be stated accurately, likewise using phosphate esters and thus negative charges.
An object of the present invention is, by contrast, to provide compounds which avoid this negative surface charge and link the oligoglycerol or sugar residues by a nitrogen atom into the structure. The positive charge on the nitrogen residue balances the negative charge on the phosphate, or even overcompensates when 2 nitrogen atoms are used in the molecule. This object is achieved according to the invention by a compound of a general formula I 
in which A 
where R1 and R2 are, independently of one another, hydrogen, a saturated or unsaturated acyl or alkyl radical which can optionally be branched or/and substituted, where the total of the carbon atoms in the acyl and alkyl is 16 to 44 C atoms,
s is an integer from 0 to 8,
c is a radical of a primary or secondary alcohol of the formula ROxe2x80x94, where R is a saturated or unsaturated alkyl radical, mainly with cis double bond, of from 12 to 30 carbon atoms,
n is an integer from 2 to 8,
R3 
a can be 1,2-dihydroxypropyl or
b can be alkyl with 1 to 3 C atoms when z is  greater than 0 or
c can be alkyl with 1 to 3 carbon atoms when nxe2x89xa02 and z=0,
m is 1 or 2,
x is an integer from 0 to 8,
y is 1 for z=1 to 5 or is 1 to 4 for z=1
z is an integer from 0 to 5.
Preferred compounds are those where 
xe2x80x83m=1, n=2, x=0, zxe2x89xa00, and R3 is an alkyl radical, do not apply simultaneously.
The structural elements used in the substances described herein can be varied at will and adapted to suit the particular use.
It is possible via structural parameter A to vary mainly the apolar portions of the molecules, for example via the chain length of the fatty acids and of the alkyl radicals. A modification of the polar portions is possible via the phosphate group, the nitrogen atom and the oligoglycerols linked thereto.
The compounds embraced by the general formula I have excellent biological properties and are used as
1) liposome constituents for specific accumulation of active ingredients in target cells,
2) solubilizers for substances which are difficult to administer intravenously such as, for example, Taxol,
3) active ingredients for cancer and protozoal diseases.
The compounds which have particular importance for the various applications are now described in detail. There are overlaps in this because disubstituted glycerols with the structural feature A may have both membrane-stabilizing properties (R1+R2 greater than 20 C atoms) and membrane-destabilizing properties (R1+R2 less than 20 C atoms). In particular, the boundary regions between membrane- and micelle-formers may be of special interest here.
It is common to all the structures that the novel molecules are simple to prepare, this being possible by reacting primary or secondary amines with epoxides. Thus, 1,2-dipalmitoyl-sn-glycero-3-phospho(N-methyl)ethanolamine with benzylglycidol results, after catalytic debenzylation and methylation on nitrogen, in a phospholipid with a lecithin-like structure which is used as liposome constituent.
Compounds with only one long alkyl or acyl chain have other interesting properties if they are linked via primary or secondary amines to epoxides, as is evident from the description hereinafter. They are excellent solubilizers for active ingredients which are difficult to administer intravenously and are in fact direct active ingredients for cancer and leishmaniasis.
The stepwise assembly, on which this invention is based, of the hydrophilic radicals of the phosphatidyl compounds of the formula I makes it possible to take an accurately defined composition of the compounds.
Thus the compound of the formula I according to the invention does not comprise a mixture of different molecules of indefinite composition and chain length; on the contrary, it is possible to obtain specifically a desired structure. This means that, if the desired product is an N,N-dimethyl-N-(2-hydroxypropyl-3,1-O,O-dihydroxypropyl)ammonium derivative with y=1 and z=2 in formula I, the compound is chemically defined and contains no portions with y=1 and z=1 or y=1 and z=3 etc. Hydroxypropyl derivatives having a wholly defined chain length and essentially free of other chain lengths are preferably used.
The compound of the formula I is, according to the invention, a homogeneous compound of defined structure. The compound is preferably more than 99% homogeneous in relation to the value of z. However, it is also possible to provide the compound with a homogeneity of more than 99.9% in relation to the value of z.
The compound preferably comprises hydroxypropyl derivatives on the nitrogen with 1 to 5 hydroxypropyl units, preferably with 1 to 3 hydroxypropyl units. Preferred in this connection are 1,3-linked linear oligoglycerol residues which are linked via a 2-hydroxypropyl radical to the nitrogen atom.
The radical for A=c with the formula ROxe2x80x94 is derived from the primary or secondary alcohol. When ROxe2x80x94 is derived from a secondary alcohol, radicals with the oxygen on the C2, C3 or C4 atom are preferred.
The radicals R1 and R2 are according to the invention preferably independently of one another hydrogen, a saturated or unsaturated acyl or alkyl racial which may optionally be branched or/and substituted, where the total of the carbon atoms in the acyl and alkyl is between 16 and 44.
The invention further relates to liposomes which contain phospholipids or/and alkylphospholipids, where appropriate cholesterol and 1 to 50 mol % of a compound of the general formula I.
The phospholipids or/and alkylphospholipids can be, for example, diacylglycerophospho compounds of defined structure. It is generally possible to employ these constituents of the lipids as compounds of defined structure.
In the case where y greater than 1, the radical xe2x80x94CH2(CHOH)yxe2x80x94CH2xe2x80x94OH is preferably derived from sugar alcohols which have 3 hydroxyl groups for y=2, 4 hydroxyl groups for y=3 and 5 hydroxyl groups for y=4. Examples of such radicals are mannitol derivatives for y=4, lyxitol derivatives for y=3 and threitol derivatives for y=2.
The liposomes according to the invention have a distinctly modified half-life in the blood circulation. The liposomes with m=1 are neutral to the outside and show increased retention times in the blood, while the liposomes with m=2 circulate for only a very short time as a consequence of the excess positive charge in the membrane.
The invention further relates to a pharmaceutical composition which contains the liposomes described above and one or more active pharmaceutical ingredients entrapped in the liposomes, where appropriate together with pharmaceutically customary diluents, excipients, carriers and bulking agents.
It is possible as a rule to use as active ingredients all active ingredients which can in fact be introduced into the plasma by means of liposomes. Preferred groups of active ingredients are, on the one hand, cytostatics, in particular anthracycline antibiotics such as, for example, doxorubicin, epirubicin or daunomycin, with doxorubicin being particularly preferred. Further preferred cytostatics are idarubicin, hexadecylphosphocholine, 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine, 5-fluorouracil, cis-platinum complexes such as carboplatin and Novantrone, and mitomycins.
Further preferred groups of active ingredients are immunomodulating substances such as, for example cytokines, with particular preference being given among these in turn to the interferons and, in particular, xcex1-interferon, substances with antimycotic activity (for example amphotericin B) and active ingredients for protozoal diseases (malaria, tyrpanosomal and leishmania infections). Taxol is likewise preferred as active ingredient.
Another preferred group of active ingredients are lytic active ingredients like those described in DE 41 32 345 A1. Preference is given to miltefosin, edelfosin, ilmofosin and SR162-834. Particular preference is given to alkyphosphocholines also with extended alkyl chains, for example erucylphosphocholine and erucylphosphocholines with increased phosphonitrogen distance.
The present invention further relates to the use of liposomes according to the invention for producing an antitumour composition, in which case the active ingredient is particularly preferably doxorubicin.
The present invention furthermore relates to the use of the liposomes according to the invention for producing a composition for influencing cell proliferation, in which case the active ingredient is a cytokine, particularly preferably xcex1-interferon.
The liposomes according to the invention are prepared by methods known per se using apparatus customary for this purpose. It is possible typically to convert a solution containing the various components of the liposome, including 1 to 50 mol % of a compound of the formula I, into a lipid suspension which is then forced under high pressure through nozzles or through perforated plates, it being possible to control the size of the resulting liposomes by the size of the orifices in the perforated plate. Suitable measures for converting a lipid suspension into liposomes are known to the skilled person. Preferably, 5 to 55 mol % of a compound of the general formula I are converted with 35 to 60 mol % of cholesterol and 40 to 60 mol % of phospholipids or/and alkylphospholipids into a lipid suspension which is then converted by suitable measures in a manner known per se into liposomes. Such known processes can also be used to produce a pharmaceutical preparation which contains the liposomes according to the invention and one or more active pharmaceutical ingredients. For entrapping water-insoluble active ingredients, the active ingredient is dissolved together with the lipid constituents while, for entrapping water-soluble active ingredients, an aqueous solution containing the water-soluble active ingredient is added to the lipid film.
The initial phospholipids are produced by processes described in the literature (DE 31 30 867 A1: Eibl et al., Chem. Phys. Lipids 28 (1981)), 1-4 41 (1986), 53-63 and 47 (1988), 47-53. It is possible here in particular to have recourse to processes described in the PCT/EP97/00749 application of 17.02.1997. Thus, the compounds according to the invention of the formula I can be prepared in the following way:
Example (A=a; n=2; m=1; y=1; z=2)
(Reaction of 1,2-dipalmitoyl-sn-glycero-3-phospho(N-methyl)ethanolamine with 1,2-isopropylidenelyceroglycidol) 
Corresponding reactions can be carried out to afford compounds with n=3-10, m=1, y=1, z=1-5. Starting compounds for x=2 and 3 are cephalins and N-methylcephalins, whose preparation has been described in detail. The reactions with the corresponding glycidols, whose preparation is described in the German patent application xe2x80x9cPhosphatidyloligoglycerinexe2x80x9d 19622224, leads to the required products, the addition being carried out in a 2-phase system of THF-Na2CO3/NaHCO3 1:1 (0.5 M in H2O; pH 9-10). However, no hydrolysis of the fatty acid esters is observed at these pH values.
To prepare the dioleoyl compounds it is necessary to prepare 1,2-dioleoyl-sn-glycero-3-phospho-(N-methyl)ethanolamine. This is achieved by the following reaction scheme: 
Unsaturated compounds are generally prepared analogously.
It is possible correspondingly to prepare compounds with n=4-8 because the corresponding terminal alkanolamines can be purchased and can be converted into the N-BOC-protected compounds.
Examples of a synthesis of liposome constituents are described below to demonstrate the experimental breadth of the present application. It is possible, as is evident from the examples, to prepare any fatty acid ester and alkyl ether combinations which vary in chain length, number of cis double bonds and degree of branching.
The RF values of the exemplary compounds 1 to 279 were determined in the system CHCl3/CH3OH/glacial acetic acid/H2O=100/60/20/5 parts by volume. They are grouped very close together, specifically as follows: